Reduced Graphene Oxide As Efficient Hole Injection Layer for Quantum‐Dot Light‐Emitting Diodes

Polyethylene dioxythiophene:polystyrenesulfonate (PEDOT:PSS) is widely used for preparing the solution processable hole injection layer (HIL) in quantum‐dot light‐emitting diodes (QLEDs), but it can cause erosion of the anode, posing a critical issue for long‐term stability. Graphene oxide (GO) is a promising candidate to replace PEDOT:PSS, but its performance is somewhat inferior to that of a PEDOT:PSS device. Here, we investigate the effect of reduction in a GO HIL on the hole injection ability and resulting QLED performance. We find that the hole current in reduced GO (rGO) HIL is one order of magnitude larger than that with GO HIL. The greater hole injection ability dramatically improves the current efficiency and external quantum efficiency of an rGO‐QLED by more than two times. To verify the underlying mechanism, we analyze the conductivity and energy barriers, and find that both the conductivity and the energy barriers vary depending on the degree of reduction of GO. We conclude that the increasing conductivity dominantly contributes to the improved hole conductivity in rGO layer. Thus, the optimization of reduction in rGO HILis an excellent approach to solve the anode erosion issue and to improve QLEDperformance, increasing the potential of applications in QLEDdevices.